Tornado damage in Washington, Ill. "A confirmed large and extremely dangerous tornado" was spotted near Washington, located about 145 miles southwest of Chicago, the National Weather Service said.

Tornado damage in Washington, Ill. "A confirmed large and extremely dangerous tornado" was spotted near Washington, located about 145 miles southwest of Chicago, the National Weather Service said. (Alexandra Sutter)

Two of the tornadoes that slammed into Illinois Sunday, Nov. 16, were rated EF-4, the category reserved for the second-most damaging twisters on the Enhanced Fujita Scale, the National Weather Service said.

The Enhanced Fujita scale is an updated version of an earlier chart to measure the ferocity of tornadoes published in 1971 by University of Chicago professor Ted Fujita.

The tornado that hit Plainfield, Ill., on Aug. 28, 1990, was an F-5. The 1967 Oak Lawn tornado outbreak on April 21, 1967, spawned several F-4 torndaoes, leaving 58 dead. The April 20, 2004, Utica, Ill., twister was rated an F-3, and the Feb. 29, 2012, tornado that hit Harrisburg, Ill., was an EF-4 with winds of 166-200 mph.

In rating the intensity of tornadoes, meteorologists and other experts study damage on the ground, along with wind speeds and other data, to rate twisters between EF0 (the weakest) andEF5 (the most intense).

The scale is as follows:

• An EF-5 tornado, capable of causing incredible damage, is characterized by three-second wind gusts between 200 and 234 mph and can level strong framed houses, according to the National Oceanic and Atmospheric Administration (NOAA). Automobile-sized missiles can fly through the air in excess of 109 yards, and trees can be stripped of their bark.

On May 3, 1999, a tornado rated as an F-5 under the original Fujita scale struck the town of Moore, Okla., killing 40 people and destroying thousands of homes. That event caused more than $1 billion in damage. On May 20, 2013, a comparable EF-5 tornado again hit Moore, killing 23 people.

The devastating tornado that struck the town of Joplin, Missouri, on May 22, 2011, killing 161 people, also was an EF-5 tornado.

• An EF-4 tornado can cause devastating damage, and is capable of leveling well-constructed homes and blowing away those with weak foundations. Cars can be thrown and largemissiles generated. Such a twister includes wind gusts of between 168 and 199 mph.

The tornado that struck Moore in 2013, ripping up at least two schools, was initially rated an EF-4 but was upgraded to an EF-5.

• An EF-3 tornado can cause severe damage, tearing roofs and walls off well-constructed homes, uprooting trees, and lifting cars of the ground and throwing them. It has wind gusts ofbetween 138 and 167 mph.

Several EF-3 tornadoes have been recorded in the United States this year, including one that touched down in Kemper County, Mississippi, in April, killing one person and injuringfour.

• An EF-2 tornado can cause considerable damage, tearing roofs off frame homes, demolishing mobile homes, overturning boxcars and snapping or uprooting large trees. Such a tornado ischaracterized by wind gusts between 110 and 137 mph.

A number of EF-2 tornadoes have struck the United States so far during 2013, in some cases causing injuries or substantial damage.

• An EF-1 tornado can cause moderate damage, with wind gusts of between 86 and 109 mph. Damage caused in such twisters includes surfaces peeled off roofs, mobile homes pushed off foundations or overturned and cars blown off roads.

• An EF-0 tornado causes light damage with wind gusts of between 65 and 85 mph. The impact can include damage to chimneys, branches broken off trees and shallow-rooted trees being knocked over.

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